Hydrodynamic Aspects of Surf-Ski Drain Scuppers
by David Hartwanger, Surf-Ski Info
A surf-ski is a unique design sit-on-top kayak, for use in the open ocean and surf zone. As a consequence the cockpit area is frequently submerged in water. Drainage appendages are located on the underside of the hull to drain the cockpit as rapidly as possible. The appendages are passive devices (i.e. no moving parts) that utilise the flow over the hull to drain the cockpit. IFS undertook a focussed programme of design and development work aimed at improving the performance of the surf-ski drain appendage or scuppers. The aim was to improve the draining ability without increasing the appendage drag. CFD methods were used to understand the relevant fluid dynamic mechanisms that could be manipulated to lead to design improvements. A series of concept designs were evaluated, culminating in an elegant bullet shaped after-body. CFD results indicated a 40% improvement in drain flow and a 60% reduction in appendage drag.
